The Guadalquivir depression, Also called the Betic depression, it is a geographical feature in southern Spain. It is a triangle-shaped plain that reaches 330 kilometers in length.
Its width reaches up to 200 kilometers and narrows more as one advances towards the east. The depression is extended by the edges of the Castilian plateau and opens by the Atlantic Ocean which is where the mouth of the Guadalquivir River is located..
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The Guadalquivir depression is located in Spain, in the Autonomous Community of Andalusia, which is the southernmost region of this country, which is located in the South of the Iberian Peninsula..
Its geological and morphological units, with all their inherent elements (relief, topography, flora, fauna, etc.), pass through five provinces, Jaén, Córdoba, Cádiz, Huelva and Seville. In its interior resides a protected area, which is the Doñana National Park.
The most important body of fluvial water that runs through this plain is the Guadalquivir River. In its final section, the marshes that have the same name appear, which are flooded both by the action of the river in its flood and by the tides of the Atlantic.
This depression is also flanked to the North by the Betic mountain range, to the South by the Atlantic Ocean, to the East and Southeast by the Penibetic mountain range, and to the West by the Sierra Morena, which separates it from the plateau..
An alpine mountain range exceeding 600 kilometers in length separates the Guadalquivir depression from the shores of the Mediterranean Sea.
The Penibético sector is the most external in comparison with the interior or Subbético sector. There is the Sierra Nevada in which there are mountains, including Pico Veleta, 3,392 meters high, and Mulhacén, 3,478 meters, which is the highest in the entire Iberian Peninsula..
It has been determined that the Guadalquivir depression originated in the Miocene. It arose as a pit that started from a subsidence in which the alpine movements ended up in the filling of tertiary sediments from the sea. This explains why this plain has a relief with shapes that present gentle undulations..
In addition, the formation of the depression coincided with the folding of the Subbética mountain range, which indicates that it had an uplift process.
In other words, in the Guadalquivir depression there was a grave that collapsed and that resulted in a canal, a corridor through which the Atlantic Ocean and the Mediterranean Sea communicated..
However, it was not until the end of the Tertiary Period that the Guadalquivir valley began to settle. This was closed in its northern section, which resulted in the deployment and redistribution of the waters that irrigated the area.
Consequently, the maritime waters of the depression were expelled with these deformations that occurred until the Pliocene period..
The Betic mountains, when rising, created a new coastline on which the Guadalquivir estuary emerged. Faced with the constant presence of river waters, the resulting landscape went through continuous erosion,
This process swept away the aforementioned Tertiary Period fill and gave way to the formation of very humid areas with abundant vegetation..
In the end, the marshes made an appearance in the last stretch of the Guadalquivir depression. The frequent flooding of this river allowed alluvial sediments to be deposited in the rainy season, in which the materials were dragged everywhere in order to form terraces and plains with terrestrial debris..
The vast majority of these materials were soft, although their hardness could be variable, which is evidenced by the topographic differences in the terrain..
As has been said before, the Guadalquivir depression is 30 kilometers long and 200 kilometers wide, which are reduced further when advancing towards the East..
To this is added an average height of 150 meters in which a scarce amount of reliefs can be observed throughout the plain, barely crowned by hills that can be seen in the alcoves near Chiclana, Jerez, Montilla and Carmona. There are also hard horizons with limestone or molasse.
However, what predominates in the depression of the Guadalquivir is not the landscape of the plain itself, but the presence of hills that are seen gently undulating.
There are abundant river valleys surrounded by terraces whose size is very diverse, although the generality is that the further one advances along the course of the Guadalquivir River, the more extensive the valleys become to the point where it becomes flat in the western area, where there are the marshes.
In addition, the Guadalquivir depression is subdivided into four units. Each one has unique characteristics in its morphology and geology..
Currently occupied by crops of olive trees and cereals, this unit has tabular reliefs (that is, reliefs in the form of tables) in which there was erosion caused by the waters of the Guadalquivir and Guadalimar rivers..
They have many witness hills (also called buttes, or isolated hills that are on a flat surface and that were the result of erosion). Often they are plains that are settled on clay soils that also contain limestone.
They are found on the left bank of the Guadalquivir river. The number of its levels is disputed, because although some authors point out that there are 17, others suggest that there are only 5.
The marshes dominate the landscape and occupy up to 2,000 square kilometers, but they have been retreating due to the fact that the marine waters have been penetrating the area through pipes and estuaries..
The coast, for its part, is very dynamic, with sections that have coastal arrows and dune cords that receive a direct impact from the marine currents from the Atlantic Ocean..
Additionally, geological materials are often soft and fertile, such as gravel, silt, sand, and clay..
This conformation of the terrain has made a good part of the valleys of the Guadalquivir depression suitable for agriculture. There are crops of vegetables, cereals, olive trees and fruits.
Consequently, it follows that this area of Spain has great importance for the nation's economy, since many of its food comes from there..
It should be noted that the Guadalquivir depression cannot be fully qualified as a plain in which plains abound, since this would be to generalize.
Although it is correct that the relief has areas without many elevations, it is also true that there are hills and hills in which the passage of time is witnessed. In other times, the water level in the Guadalquivir was much higher, and as it eroded the land, it excavated it to form terraces and valleys..
The Ebro depression is a valley in Spain that is northeast of that country. The river Ebro runs through it. It has been compared in importance and characteristics with the depression of the Guadalquivir, and with good reason, since they share many features in common, although it is worth mentioning only the most notable.
Apart from their large size, both depressions share their triangular shape, their coverage by sediments from the Tertiary Period and their complex irrigation of river waters..
To that short list of similarities is also added the low relative altitude of the depressions, their relevance to the Spanish, and not to mention their pronounced antiquity..
However, the depression of the Guadalquivir and that of the Ebro also have countless quantitative and qualitative differences. Because they are as punctual as they are specific, they do not fully fit here, so only three of them are considered substantial: the geological era, the type of fill and the appearance of the valleys..
The Guadalquivir depression ends its formation at the end of the Miocene, while the Ebro depression did so in the Oligocene. However, both depressions were appearing within the framework of the alpine folding.
The Ebro depression has an endorheic fill with sediments that form lakes that remain within the continent, while the Guadalquivir depression is more exorheic, that is, the surfaces of its coasts are dominated by the waters of the sea..
In the depression of the Guadalquivir there are landscapes of soft countryside whose rains fall less frequently than in the fields of the depression of the Ebro, where by the way it is possible to find bad lands and formations of ravines..
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